The invention relates to a process and a device for coating substrates in an in-line coating system comprising at least two evaporation devices, each with an evaporator tube.
In the mass production of organic semiconductors from so-called “small molecules” for use in illuminants, in monitors, in photovoltaics, in electronics, or in other products the carbon evaporation of two or more organic materials is of great importance.
This applies in particular to the emission layers of OLEDs (Organic Light Emitting Diodes) and to the absorber layers of OSCs (Organic Solar Cells) as well as to the doped charge transport layers which can also often serve for the injection of charge carriers.
In many cases a constant stoichiometry of two or more organic materials within one layer of a multi-layer component is desired. On the other hand, there are cases in which 100% of one material is to be deposited on one boundary surface and, for example, only 10%, or even only 0%, is to be deposited on the other boundary surface. A whole array of factors, such as optimal charge carrier injection (100% portion), good charge transport (10%), or chemical incompatibility with the material of the adjacent layer (0%), can play a role here.
The next-to-last case is in general achieved by first only one material being deposited for a first layer (100% portion) and subsequently a carbon evaporation of the same material (10% portion) in combination with a second material (90% portion) being carried out for a second layer.
The abrupt transition of the stoichiometry between the first and second layer or the different morphology of the respective layer can possibly be unfavorable for the function of the component. Thus in these cases a third layer is deposited between the first and second layers, which has a stoichiometry corresponding, for example, to the average value of the stoichiometric ratios of the first and second layers.
In the manufacture of the components in a cluster system only two vapor sources are required for the three layers, said vapor sources being switched on and off in a temporal sequence. In production systems, on the contrary, reasons of cost demand greater throughput, which can in principle be achieved with in-line or roll-to-roll systems. The consequence is however that for the latter two types of systems a total of five vapor sources are required (three for material 1 and two for material 2) and thus the complexity, or the costs, of the system are increased.
Going beyond the three-layer system it would possibly be desirable to attain a gradual transition of the stoichiometry or morphology instead of a stepwise transition.
Moreover, it would also be of interest in an in-line or roll-to-roll system to keep the stoichiometry in a layer as constant as possible.
From the state of the art various possibilities for producing gradient layers on substrates are known.
Thus, DE 10 2004 014 323B4 discloses a process for producing a gradient layer or layer sequence on a substrate. Therein the deposition of at least two materials within one coating compartment is accomplished by sputtering with two magnetron cathodes, each of which carries a target. In so doing, a mixed layer arises in the transition area from the first to the second target. Furthermore, baffles are provided which, independently of one another, permit a shielding of the target with respect to the substrate.
A similar development is disclosed by U.S. Pat. No. 6,488,824 B1, in which two magnetron cathodes are also disposed which, by means of shielding, make possible a transition area of the two targets. In this way a constant mixed layer can be deposited.
The disadvantage of using sputtering systems for producing gradient layers preferably of organic materials lies in the fact that they are usually destroyed by the sputtering process, on account of which sputtering is not suitable as a method of deposition of organic materials.
Consequently, for organic materials, an evaporation is carried out in a crucible. Typical state-of-the-art vapor sources of in-line systems or roll-to-roll systems are tubes in which vapor exiting from a crucible is uniformly distributed. The tubes comprise a plurality of nozzles which are disposed in a row transverse to the direction of advance of the substrate. In the carbon evaporation of two (organic) materials, two tubes, one for each of the respective materials, customarily emit vapor through their nozzles onto the substrate.
DE 103 12 646 A1 discloses a process for producing a converter layer, where in that process an organic converter material is mixed into an inorganic matrix. This is achieved by intersecting vapor deposition of the two materials. These are heated and evaporated in two different vapor deposition devices, where the resulting vapor lobes intersect and form a common vapor deposition zone. For a continuous vapor deposition the two vapor deposition devices have a fixed orientation relative to one another.
The mixed layer thus achieved has a uniform structure and under no circumstances permits a flexible change of the gradient profile.